the demo won't run, says my pc is 64 bit ? will the retail (gog) version run on my 64 bit windows 7 system ? thanks

Depends on what demo you're talking about as I can't seem to find one. The versions available at icemark.com are fullblown DOS versions of the games so you need to run them with DOSBox. The remakes available here are listed to be compatible with Windows (XP, Vista, 7, 8) and Mac OS X (10.7.5 or newer). 64-bit OS should be able to run 32-bit applications (most games and programs around are actually 32-bit applications. There are very few purely 64-bit programs around.)